Most people will only notice an interior fireplace or an exterior chimney but there are many components that work together to keep your system functional and safe. Becoming familiar with what makes up a chimney and the terms used to describe each part are useful for maintenance or if you notice an issue with your system. Having general knowledge of the terminology will facilitate clear communication between you and a chimney professional, but ultimately, the technician evaluating your system will be able to guide you through the specifics of your system. See our chimney anatomy reference guide below to prepare for your next annual inspection.
- Chimney Cap – Made of heavy duty stainless steel, a chimney cap protects your system from animals and debris entering your chimney or home. In addition to keeping harmful elements out, a chimney cap also protects your roof by keeping embers and sparks in.
- Flue – A flue is the channel for exhaust gas to safely exit from an appliance or fireplace to the outdoors. A flue ensures that no smoke or carbon monoxide leaks out of the chimney from a heating system or appliance. You may have multiple flues on your property because they are used for several appliances, such as ducts, pipes, vents or chimney/fireplace systems. A flue is typically made from terra cotta clay or a stainless steel liner. To function properly and keep your home safe, a clay flue must not have any cracks or missing mortar between the joints and a stainless steel liner must be free of any holes or large gaps at the pipe seams.
- Smoke Chamber – A smoke chamber is the cavity just above your firebox. It angles from the wide area of your fireplace to the narrower opening to gently compress the byproducts of combustion into a smaller space without causing backdraft. Older smoke chambers are made of brick in a stepping pattern. The CSIA recommends that all smoke chambers have smooth walls, and most building codes require it. The stepping pattern of older smoke chambers can obstruct your chimney’s draft, causing the smoke to flow back into your home and more heat transfer between your fireplace and the surrounding home structures.
- Smoke Shelf – The smoke shelf is right behind the chimney damper which looks like a flat surface or curves inward and up towards the flue. It creates a thermal barrier by filling the space behind the firebox with brick or rubble and then topped with a flat or concave area that is parge coated. The smoke shelf catches rain water and falling debris and helps with the effective transition of large smoke volume entering into the small space in your chimney. It also helps prevent downdraft in your chimney from entering your home.
- Firebrick – Firebrick’s main ingredient is fireclay, which contains alumina and silica. Both these elements are capable of withstanding high temperature. Firebricks can withstand repeated heating and cooling at various temperature ranges because the ceramic, ferric oxide and other chemical additives absorb, and do not transfer, high temperatures. The low thermal conductivity offers greater energy efficiency and insulating value.
- Lintel – Lintels are a horizontal beam placed across the fireplace opening as structural support for the chimney. It plays a crucial role in supporting the chimney’s weight and protecting other components from the high temperatures of a fire.
- Hearth(inner/outer-extension) – This is the floor of the fireplace. The two sections of the hearth is the inner and the outer or hearth extension. The inner hearth is the space in which the fire actually burns and handles the potential corrosiveness of the burned materials and high heat it can be subjected to. The outer hearth or the hearth extension is the floor right outside of the firebox. It is important the extension is made of heat resistant materials such as tile or brick to reduce the chance of fires.
- Ash dump door – Ash dump doors are small brick-sized doors located at the bottom of some fireplaces. They allow you to sweep ashes into an ash dump located through the doors under your fireplace. Often, the ash dump door needs frequent replacing due to intense heat and corrosion damage.
- Ash dump – An ash dump is a compartment in some fireplaces directly below the ash dump door where you can place old ash residue. It’s often surrounded by concrete and allows easy sweeping of ashes and embers after a burning session.
- Clean out door – The clean out door is used to clean out the ash dump. If your system has an ash dump, the clean out door is usually located outside or in the basement to make ash removal easy.
- Mantel – Today a mantel is used as a shelf to display photos, home decor or hang stockings, but the initial purpose and design was a hood over the fire grate to catch smoke and prevent it from entering the home. Because of the improvements made to the design and system, the mantel serves an aesthetic purpose, such as helping the fireplace stand out and become the focal point of the room. The mantel may cover the lintel and any joints around the top of a fireplace opening between the firebox and the wall of the chimney breast.
- Firebox – The firebox is where the magic happens! This is where you build a fire and because this Is the area in direct contact with the heat of the fire, it is important to make sure that the firebrick has not weakened or cracked.
- Crown – The chimney crown acts as a roof for your chimney and protects the chimney from water damage entering through small cracks. The crown is made of cement and has a sloped design to provide a solid barrier against water infiltration. Water damage is one of the most common issues for the brick and mortar used to build a masonry chimney. It is important to repair cracking and decomposition on your chimney crown quickly to maintain the structural integrity of the chimney.
- Masonry shoulder – The shoulder is the exterior sloped area where the chimney begins to narrow. Similarly to the smoke chamber, masonry shoulders were built with a stepping pattern which is prone to water damage and leaks. When repairing or rebuilding the shoulder, consider a sloped smooth design or using a mortar or concrete seal.
- Flashing – Chimney flashing is a waterproofing measure installed where the chimney meets the roof. The flashing is made up of step flashing, counter/cap flashing and base flashing. Step flashing is a thin metal sheet which lies under the roofing shingles and is embedded into a groove in the chimney brickwork. Counter or cap flashing is a thin L shaped metal which covers the step flashing and is also embedded into the chimney brickwork. Base flashing is the top layer which seals the point where the vertical chimney meets the roofline. These three components along with caulking create a waterproof seal and protect your roof and chimney from moisture penetration.
- Chase Pan – Also known as a chimney chase cover, a chase pan is a metal cover that seals the top of the chimney structure. You will often find a chase pan on framed wood or siding prefabricated chimneys, but they are also a great alternative for replacing a cement crown on masonry chimneys.
- Chase – A chimney chase is another name for a prefabricated chimney which is usually built of framed wood or siding. The chase provides an enclosure for a fireplace’s stainless steel flue and fuel-fired appliances like a furnace.
- Damper – Chimney Dampers are lever activated doors within your chimney which can be closed to prevent energy loss when your fireplace is not in use, as well as help prevent rain water or animals from entering your property.
- Footing – Larger fireplaces may require a structural footing, which is a poured concrete footing below frost level. Depending on the size of the fireplace, an existing patio may not be sufficient to support the weight. Typically, the footing is the surface under the ash pit in older homes or under the firebox in homes without an ash pit.
- Foundation – Chimney foundations are usually attached to the house’s foundation beam along one side. It is made of heavy-duty brick or cinder block and provides the structural support for the chimney’s walls.